CaribSea LifeRock Shapes is made of an aragonitic base rock, instead of the typical cement used by some other artificial rock creators. Every rock contains a network of micro and macro pores that intertwine within the rock's internal structure, creating the perfect environment for natural nitrifying bacteria. LifeRock is manmade. Every LifeRock from CaribSea has an artificial coating and texture that mimics natural coralline algae after being in the ocean for years. Every box of Shapes LifeRock contains a mixture of arches, rings, and tunnels giving you unique looking pieces that can be used on their own or as accents to the rest of the aquascape. Pieces are unique. They will look similar to the pieces picture, but every box is different. 5 to 8 pieces are included in every box of LifeRock Shapes. We guarantee every box is at least 20 pounds. We recommend 1 to 2 pounds of rock per gallon of aquarium water. NOTE: This rock is fragile and may break in shipping. Unless it is pulverized we can not replace the rock if broken. This rock needs to be glued together when placed in an aquarium anyway, and in many instances you might want to break the rock into smaller pieces to build a desirable structure.